The present invention relates to a method and an apparatus piecing up broken yarn in an open-end spinning system. The most important feature of the present invention is that the yarn end ready for yarn piecing up is introduced at each piecing up operation into a rotor after the lapse of a predetermined time since the rotor which has so far been braked is released from the braking pressure and started into revolution. When the rotor is released from its brake shoe and contacted with a moving belt, the rotor is revolved with a gradually increasing speed until it reaches a designated speed.
According to the present invention, the yarn end is introduced into the rotor while the latter is still in the course of its acceleration. When the rotor is revolved at an extremely high speed, as for instance at 70,000 r.p.m., the yarn end is twisted instantly due to high-speed revolution of the rotor when the yarn end is introduced into the rotor for piecing up. Moreover, the yarn is subjected to a high shearing stress due to the large centrifugal force caused by the rotor revolution, thus causing twist breakages. In effect, with 70,000 r.p.m. of the rotor, the rate of successful yarn piecing up is reduced at most to 1 percent. The present invention envisages to obviate such inconvenience by introducing the yarn end into the rotor for joining with the fiber material while as yet the yarn end is not twisted sufficiently and the centrifugal force exerted to the yarn end has not attained the maximum value.